This invention relates to circuitry for processing electronic signals, which convey information in vector form. An example of such a signal is the chrominance component of composite video signal.
The invention, in part, is directed to determining the magnitude of a vector of a sampled signal. If respective samples of a signal are orthogonal components of a vector, the magnitude of the vector may be determined by forming the square root of the sum of squares of the orthogonal components. While the function may be straightforward to calculate on a computer, it is difficult to realize circuitry which can perform the function at video sample rates. If respective signal samples are not orthogonal components of the vector, the sum of squares algorithm will not produce the desired result at all.
Comb filters are the preferred circuitry for separating frequency-interleaved components of video signals. Of these, three line adaptive comb filters provide the best cost-performance trade off. The three line adaptive comb filter uses two one line delays to concurrently provide signals from three successive video lines. Adaptive control circuitry determines the proportions of video signal from the first and last lines to be combined with video signal from the middle line to produce separated video signal components.
Under certain signal conditions an adaptive comb filter will produce undesired hanging dots. It has been determined that control signals generated using the magnitude of vectors representing chrominance information in the respective lines may be utilized to minimize undesired hanging dots output by adaptive comb filters. Thus there is a need for apparatus to generate magnitudes of vectors at video rates. A need will also be demonstrated for a method and circuitry to generate magnitudes of vectors in sampled signals where respective samples are not orthogonal components of the vector.
A method of generating the magnitude of a sampled vector includes weighting a plurality of successive samples to produce a like plurality of magnitudes of weighted samples, determining the magnitude of the largest of the plurality of samples, weighting such magnitude to produce a maximum sample value, and summing the plurality of weighted samples and the maximum value.
Apparatus for determining a vector magnitude includes a tapped delay line for concurrently producing a plurality of samples. Respective weighting circuits are coupled to the respective taps and weighted samples are coupled to a first signal summer. A maximum detector is coupled to the respective taps for selecting the largest sample value. This sample value is weighted and applied to a further signal summer wherein it is added to the signal output from the first signal summer.
Exemplary utilization of this method and apparatus is found in an adaptive comb filter where the ratio of the magnitude of the chrominance component vector from a middle line of video signal to the average magnitude of the chrominance component vectors from first and last lines of video signal is used to control a soft switch to alter the content of separated luminance signal.